docker-swarm: migrate to Homebrew/homebrew
docker-swarm: migrate to Homebrew/homebrew

Has been accepted into the main repo due to the non-dev release. See:
https://github.com/Homebrew/homebrew/pull/37874

DomT4/homebrew-devel-only,Arthur2e5/homebrew-devel-only,keithpitty/homebrew-devel-only